1. Field of the Invention
This invention relates to an active memory control method having built-in data processing function and more particularly relates to a memory control method which is capable of implementing data format conversion internally and an active memory which uses this memory control method.
2. Description the Prior Art
As computer systems have been spread, various data are digitized and stored in a computer system. Various media such as magnetic disks, magnetic tapes, MO, and CD-ROM are used, however, the magnetic disk is mainly used because of capability of high rate random access and readable/writable performance, and low cost per capacity. Magnetic disk apparatus for storing data given from the outside in a magnetic disk and reading and sending out data from a magnetic disk in response to a request from the outside has been widely used.
Because in the conventional magnetic disk apparatus the data input/output unit is a physical unit called as block, it is necessary that a magnetic disk apparatus is connected to a server side computer system (referred to as sever computer hereinafter) and the server computer manages the data input/output to the magnetic disk apparatus to use the data stored in the magnetic disk apparatus by use of a client side computer system (referred to as client computer hereinafter). Then, the server computer manages the magnetic disk apparatus and processes a request from the client computer, such system is called as SAD (Sever-Attached Disks).
Assume that many client computers in which various data are used by way of a network is addressed. The environment is used as a premise for the client server system which is typical of various systems widely used as the network technology has been progressed, and now the environment becomes the most popular. It has been revealed as a problem that the server computer is a bottleneck in SAD in the environment to restrict the scalability of the whole system. For example, in xe2x80x9cFile systems for Network-attached Secure Disksxe2x80x9d by Gibson, D. F. Nagle, K. Amiri, F. W. Chang, H. Gobioff, E. Riedel, D. Rochberg, J. Zelenka, Technical Report CMU-CS-97-118, Carnegie-Mellon University (referred to as literature-1 hereinafter), it is described as an experimental result that, when files on a server computer is accessed by clients by means of NFS (Network File System) service, SAD performance cannot accommodate four or more pairs of client and magnetic disk apparatus. In this case, the majority of the process performed in the server includes I/O process to the magnetic disk apparatus, data conversion process in the server computer, and communication process between the server computer and client computers.
In view of such situation, a method in which a client computer takes access to the magnetic disk apparatus not by way of the server computer to use data is proposed in order to improve the scalability of the whole system. For example, in NASD (Network-Attached Secure disks) system described in the literature-1, data is transferred directly from a magnetic disk apparatus to a client computer system which received an access right from the server computer in the unit of logical object to improve the scalability of the whole system.
Furthermore, in Active Disk described in xe2x80x9cActive Storage For Large-Scale Data Mining and Multimedia Applicationsxe2x80x9d by E. Riedel, G. Gibson, C. Faloutsons, Technical Report CMU-CS-98-111, Carnegie Mellon University (referred to as literature-2 hereinafter), a part of process performed in the server heretofore such as edge cutting of a image is performed in the magnetic disk apparatus side to thereby improve the scalability of the whole system.
In the case that a system is structured so that a part of process is performed in a magnetic disk apparatus, if a unit for performing this process is incorporated statically in the magnetic disk apparatus, then switching processing unit and method, depending on current system load, computer resource to be used, and application, becomes difficult. If a module for performing process as a hardware is incorporated for realizing these process, it is necessary to design and fabricate different units for each processing, and these units cannot be general purpose units, and the development cost will be high.
The magnetic disk apparatus in which the data is transferred directly between a client computer and the magnetic disk apparatus not by way of the server computer will improve the system scalability, however, when the data is used actually by a client computer, an extra process is required to convert the data format to a data format desired by the client.
Accordingly, it is the first object of the present invention to provide a mechanism for converting the data efficiently to a data format required by a client computer, and to provide an active memory unit (for example, magnetic disk apparatus) which is capable of reducing the load on the client computer and a network.
Furthermore, it is the second object of the present invention to improve the cost performance ratio of a magnetic disk apparatus having the data conversion function.
To achieve the first object, in the present invention, a data request analysis unit for accepting a request from a client computer, a data conversion program generation unit, and a data conversion unit are provided in the internal of an active memory unit (for example, magnetic memory unit).
A data conversion program generation unit generates a data conversion program based on the analysis result obtained by the data request analysis unit. The data conversion program generation unit first retrieves a program module required to generate the conversion program among a group of program modules stored in the magnetic disk apparatus to generate the data conversion program corresponding to the request of the client computer. If there is no suitable program module in the magnetic disk apparatus, the program module is retrieved from the client which requested the data or a computer (referred to as program module server hereinafter) which manages a group of program modules, the program module is downloaded by way of a network, the program module is combined to generate the data conversion program.
The data conversion unit downloads the conversion program generated by the data conversion program generation unit, converts the data read out from the magnetic memory medium by use of the program, and transfers the type converted data directly to the client computer by way of the network interface. Furthermore, a buffer management unit is provided between the data conversion unit and the network interface to cope with congestion of the network and the converted data is cashed and re-transmitted as required. If the request from the client computer is a copying of the converted data to another memory, the converted data is transferred to the memory to which the copying is addressed by way of the network interface.
To achieve the second object, the active memory (for example, magnetic disk apparatus) should be rendered usable for general purpose. In detail, a method in which hardware to be used exclusively for respective processes are designed and manufactured results in high cost per one hardware, and the cost performance ratio cannot be high. To improve the usability for general purpose, a method in which the necessary data conversion process is described in a software as a program by the server computer or the client computer and data conversion program is executed on the magnetic disk apparatus is employed. As described herein above for the means to achieve the first object, if there is no suitable data conversion program on the magnetic disk apparatus, the data conversion program is downloaded in the form of a program module by way of the network, and the data conversion program generation unit combines the program module to generate the data conversion program.
The following and other objets, advantages, manner of operation and novel features of the present invention will be understood from the following detailed description when read in connection with the accompanying drawings.